On Mon, 8 Mar 2004, Bob Barr wrote:
> IR reflection from the bottom of the pieces may be sufficient if you
> have a transmitter/receiver pair under each square. From a known
> starting arrangement, it shouldn't be necessary to have each piece
> uniquely identify itself.

Furthermore, anyone who play chess with a real chess set know that capturing
of oppenent's chessman could be completed in several ways. Example remove
the chessman to be captured first, then move your own chessman over there.
Or you could move your chessman to displace the oppenent one, and finally
remove it from the board.

Furthermore, anyone who play chess with a real chess set know that capturing
of oppenent's chessman could be completed in several ways. Example remove
the chessman to be captured first, then move your own chessman over there.
Or you could move your chessman to displace the oppenent one, and finally
remove it from the board.

> Resend. Hit the send button too soon.
>
> Furthermore, anyone who play chess with a real chess set know that capturing
> of oppenent's chessman could be completed in several ways. Example remove
> the chessman to be captured first, then move your own chessman over there.
> Or you could move your chessman to displace the oppenent one, and finally
> remove it from the board.
>
> Can this situation be handle?
>
> Regards,
> WH Tan
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways. See http://www.piclist.com/#archives for details.

> Make the chessboard an array of 64 push-buttons. Every move you'll
>have to press the square you are leaving and press again the square
>you'll arrive.
>
> Mark Jordan, PY3SS
>
>
>On 9 Mar 2004 at 23:50, WH Tan wrote:
>
> > Resend. Hit the send button too soon.
> >
> > Furthermore, anyone who play chess with a real chess set know that
> capturing
> > of oppenent's chessman could be completed in several ways. Example remove
> > the chessman to be captured first, then move your own chessman over there.
> > Or you could move your chessman to displace the oppenent one, and finally
> > remove it from the board.
> >
> > Can this situation be handle?
> >

> Every move you'll have to press the square you are leaving and press
> again the square you'll arrive.

Since Olin's not here anymore, I'll take his place.

This is not the only poster who has grandiosely proposed a solution
that the original poster specifically mentioned they considered
insufficient. Nor is this the only thread where this has occurred; the
flood of responses telling the owner of a flash PIC that UV-erasable
parts could not be unprotected was amusing. In a sad sort of way.

If you're going to take the time to post a response, you ought to at
least read the original message. Carefully.

Grr. (How'd I do? Too nice? Not enough name-calling?)
(Not that I've never done the same. Sometimes a thread gets well along
before I see something that I feel deserves a response, by which time
the original message is long gone from MY mail files. Which is some
excuse, I guess...) (And of course, at some point it is better to get
somewhat unhelpful answers than no answers at all.)

anyway...

If you think you can make reliable contact between the chesspieces and
at least two contacts on each square of the board, I think I'd feel a
lot better about some sort of digitial signal (dallas one-wire PROMS?)
than analog. Getting reliable low contact resistance, as you'd need
for different resistors to identify the pieces, is tricky. I think.)
(so how many unique identifiers do you need anyway? One for each piece
of each color? Or as few as one per each type of piece of either
color?) (I really like the idea of an IR-transparent chessboard...)

I held off on this, but here's a solution that will work perfectly -
providing you don't mind the relatively high cost and complexity. Whether
this is worthwhile depends on whether this is a one off or many off and how
bullet-proof you want it to be.

Each piece contains half a small pot core in its base with the open face
pointing downwards towards the board.. Wind coil on core and resonate at a
target frequency. Power will be provide to this coil from the board. Diode
rectify output from resonant circuit and smooth resultant DC with a filter
capacitor. All pieces identical to this point.

Under each square is a similar core (may be larger radius) that can be
driven at the resonant frequency. When it is, the coil in the piece can be
used to provide power.

Each piece has it's own electronics which are enabled when the piece is
powered via the coil. The enthusiastic can try to signal back across the
coil link while it is producing power (I have done it) but I would strongly
recommend providing a powering pulse and then responding when power is
removed. Such signalling could be as simple as a clock driven counter (eg
CD4017) with outputs arranged to control a responder and coded differently
for each piece. However, if you use this solution then a dedicated processor
per piece probably makes sense.

Rather than switch drive to all 64 squares in turn you could drive eg rows
and columns so that 8 sink and 8 source drivers handled a whole board.
"Listening" handled similarly.

With this arrangement you can tell what is on every square.
Some design will be required to handle all legitimate orientations of piece
on square.
I believe that if all pieces were within a square (as they should be) then
the design would not be too hard.

This is a time consuming solution to implemenmt as a one off but liable to
be one of the best as it provides an essentially "perfect" solution.

dear Russell McMahon
i like your way...
using resonators into each piece (tuned on 32 different frequencies to
identify the piece), activated (a simple magnetic switch) by the chess
scanner (small coils under each square, to identify the location over the
chess board) and induced to resonate by a general low frequency transmitter
(coil around the board, that generates a frequency sweep and detects the
power absorption due to the piece resonance [parallel resonance]).
Should be cheap and simple enough for everybody... :)
at least a good start.
All best everybody

In my opinion the BEST way is to use SMD IR Transmitter/Receiver packs.
They are about the size of a ladybug beetle. The way they work is that
mounted on a PCB below the chessboard is as many of these as there are
squares. The IR xmttr and the IR sensor are tilted slightly toward each
other. They are about $.50 ea. NOTHING is mounted in the chess piece,
although their bottom MUST be flat.

These sensors have a 60mil" range. Anything within 60mil" above the
sensor will reflect the IR and be considered PRESENT. When the piece is
removed and placed elsewhere, it momentarily breaks the beam, which no
longer has a reflection. The surface needs no special texture or
anything, the IR will bounce off of almost everything.

While the IR sensors are also slightly affected by strong lights or
sunlight, the circuitry easily detects a reflection from a steady beam
by turning on and off the beam; if the signal is seen while the IR beam
is off, its a bogus signal and is ignored. The bogus extraneous light is
blocked when the piece is placed back down... so it can operates in very
strong light.

To save the IR emitter life, I only drive it every 40ms for 20uS on a
rotating basis. Works great.

> i like your way...
> using resonators into each piece (tuned on 32 different frequencies to
> identify the piece), activated (a simple magnetic switch) by the chess
> scanner (small coils under each square, to identify the location over the
> chess board) and induced to resonate by a general low frequency
transmitter
> (coil around the board, that generates a frequency sweep and detects the
> power absorption due to the piece resonance [parallel resonance]).

OK - that's different from my way - and should be workable. Presumably you
mean that each square has its own coil which can be excited individually.
This could use a row and column system as I proposed so you only need 16
switches. You select each square in turn and scan across all frequencies
looking for a resonant load. In each case you could start off with the
frequency of the piece that you expected to be there - this would limit
searching time. You could use 32 frequencies for unique identification of
every piece or only 12 to represent the 2 sets of 6 types of pieces.
Should be reasonably easy to implement. Tuning each piece could be achieved
with standard capacitor values and numbers of turns on the inductors.

> Ok, Ok, I've watched this chessboard thing all day. Gotta rescue ya...<g>
>
> In my opinion the BEST way is to use SMD IR Transmitter/Receiver packs.
> They are about the size of a ladybug beetle. The way they work is that
> mounted on a PCB below the chessboard is as many of these as there are
> squares. The IR xmttr and the IR sensor are tilted slightly toward each
> other. They are about $.50 ea. NOTHING is mounted in the chess piece,
> although their bottom MUST be flat.
>
> These sensors have a 60mil" range. Anything within 60mil" above the
> sensor will reflect the IR and be considered PRESENT. When the piece is
> removed and placed elsewhere, it momentarily breaks the beam, which no
> longer has a reflection. The surface needs no special texture or
> anything, the IR will bounce off of almost everything.

How do you know what piece is where with that way?
Does the OP want that? I haven't seen much of the thread.
David...

My cousin's kids have a toy (ingenously designed, I feel) that consists
of something that looks not unlike a Speak-n-Say, only instead of
pulling a string (that breaks on day 2 of ownership), the child places
an object in a hole. The toy then announces the name of that
object in the language du jour (different cartridges available), and
either makes excited happy noises if it was the right object or
repeats the name of the one it wanted.

It broke, and I was (of course) tasked with fixing it. The really
neat thing is how it works (aha! The point arrives!).

Each cartridge contains a small processor and a card-edge connector.
Each object contains a resistor. The main unit is only a speaker, an
amplifier, and batteries/power regulation. When a toy is placed in
the hole, it is guided to its proper resting place by, well, being stuck
in a hole. There's a metal plate in the bottom of the toy which
pulls a magnet up against its underside, closing a switch, which lets
the processor know that a new object has arrived. On the bottom
of the object are also two little metal contacts, which touch a pair
of concentric metal rings. Those serve as the contact points for,
you guessed it, a precision resistor.

My point here is that this toy is CERTAINLY treated far rougher
by my 2 and 4 year old cousins than an electric chess board, and
the resistor trick works quite well for it. Rather than seating the
pieces in a hole, have a little plug on the bottom that fits into
a hole on the board. The magnet beneath not only serves to
close the switch and notify the processor of a change, but
also to pull the piece down tight.

For anyone who made it this far and still cares, the toy is called
a "Little Linguist."

>If you think you can make reliable contact between the chesspieces and
>at least two contacts on each square of the board, I think I'd feel a
>lot better about some sort of digitial signal (dallas one-wire PROMS?)
>than analog. Getting reliable low contact resistance, as you'd need
>for different resistors to identify the pieces, is tricky. I think.)
>(so how many unique identifiers do you need anyway? One for each piece
>of each color? Or as few as one per each type of piece of either
>color?) (I really like the idea of an IR-transparent chessboard...)
>
>BillW

>> Every move you'll have to press the square you are leaving and press
>> again the square you'll arrive.
>
> that the original poster specifically mentioned they considered
> insufficient.

More on this: I initially cannot see why this solution is not good
enough, but the person who asked me the possibility to build such a
board is a (good) chess player, and explained me that sometimes, for
instance during a timed match, two pieces can fall down and then
returned to the board not in their original places because of the hurry
of the time countdown. Even if any of the players notice that, it can be
too later and the referee can order to continue with the match as is.

So in this case, a board that really knows which type of piece has on
each square should be very helpfull.

Which might rule out some options unless you have the PIC
wait for a settling time. For instance, as a magnet approaches
a sensor the sensor will see an increasing field. When does the
PIC decide that the piece has been placed ? Perhaps when the
timer is struck ? That would also eliminate false positives from
hovering-but-unplaced pieces

>Robert Rolf wrote:
>
>> What Jinx suggested, a resonant coil under each square
>[...]
>> And the idea of using hall effect and having different
>[...]
>> One could also use an IR transparent base and a reflective
>[...]
>
>This are the three methods we have.
>
> > Do let us know what you discover works best.
>
>Sure, if we continue with this project. Of course it will need a PIC too.
>
> > My bet is hall effect with enough variance in the
> > magnet strengths that position error is within the
> > 12 quantizing levels you'd need. Or IR.
>
>I agree. I do not like too much the radio method due to the
>interferences, either internal between chessman's coils, either external
>noises (mobile phones).

Permanent magnets can have significantly differing strengths due to the way they are magnetised.
Hall effect sensors have significant tempco, and of course there is the earth's magnetic field, and
local magnetic fields to contend with. This would also be somewhat expensive.

My money's still on my earlier suggestion of a simple tuned circuit in each piece, and coils etched
into a PCB under the board - cheap & easy to build. Even if you couldn't figure out a way to do it
in a matrix, the switching would only need nine 8-1 analogue multiplexers (ultra-cheap 4000 CMOS) ,
and the detection hardware would be simple and cheap - PC generates the frequencies, and a simple
detector generates a DC level for the PIC ADC to detect the presence of a piece - maybe a handful of
passives and an opamp. Can't see how you could get much cheaper than this.

You could even make it retro-fittable to existing pieces, as you could usea PCB coil with a cutout
for the capacitor, forming a simple disc shape that can be stuck to the bottom of the piece.
Proximity of the piece will not cause false detection (e.g. if piece hovers) - you are simply
looking for a resonance at one of 12 frequencies. The position of the piece within the square should
also not be much of a problem. The proximity of the board coil to the (pcb) coil in the base of the
piece would be so close (2-3mm max) that cross-coupling to an adjacent piece should not be an issue.

Even if PCB coils turn out to not give enough coupling at a suitable frequency, small surface-mount
inductors could be used - still cheap, and very good coupling - I've recently used these to do an
inductive datalink into a potted product.
--http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listservEraseME.....mitvma.mit.edu with SET PICList DIGEST in the body

I'm curious. Do you want to detect only whether a piece is present on a
square and identify the square, or whether or not there is a piece present
on a specified square and whether it is a bishop, queen. pawn,... etc. Or do
you want to create a record of all of the moves of all of the peices on the
respective squares so as to reconstruct the game. I apologize if this has
been explained already, but I have no followed the thread.

>
> On Thu, 11 Mar 2004 00:33:54 +0000, you wrote:
>
> >Robert Rolf wrote:
> >
> >> What Jinx suggested, a resonant coil under each square
> >[...]
> >> And the idea of using hall effect and having different
> >[...]
> >> One could also use an IR transparent base and a reflective
> >[...]
> >
> >This are the three methods we have.
> >
> > > Do let us know what you discover works best.
> >
> >Sure, if we continue with this project. Of course it will need a PIC too.
> >
> > > My bet is hall effect with enough variance in the
> > > magnet strengths that position error is within the
> > > 12 quantizing levels you'd need. Or IR.
> >
> >I agree. I do not like too much the radio method due to the
> >interferences, either internal between chessman's coils, either external
> >noises (mobile phones).
>
> Permanent magnets can have significantly differing strengths due to the way they are magnetised.
> Hall effect sensors have significant tempco, and of course there is the earth's magnetic field, and
> local magnetic fields to contend with. This would also be somewhat expensive.
>
> My money's still on my earlier suggestion of a simple tuned circuit in each piece, and coils etched
> into a PCB under the board - cheap & easy to build. Even if you couldn't figure out a way to do it
> in a matrix, the switching would only need nine 8-1 analogue multiplexers (ultra-cheap 4000 CMOS) ,
> and the detection hardware would be simple and cheap - PC generates the frequencies, and a simple
> detector generates a DC level for the PIC ADC to detect the presence of a piece - maybe a handful of
> passives and an opamp.
> Can't see how you could get much cheaper than this.
>
> You could even make it retro-fittable to existing pieces, as you could usea PCB coil with a cutout
> for the capacitor, forming a simple disc shape that can be stuck to the bottom of the piece.
>
> Proximity of the piece will not cause false detection (e.g. if piece hovers) - you are simply
> looking for a resonance at one of 12 frequencies. The position of the piece within the square should
> also not be much of a problem. The proximity of the board coil to the (pcb) coil in the base of the
> piece would be so close (2-3mm max) that cross-coupling to an adjacent piece should not be an issue.
>
> Even if PCB coils turn out to not give enough coupling at a suitable frequency, small surface-mount
> inductors could be used - still cheap, and very good coupling - I've recently used these to do an
> inductive datalink into a potted product.
>
> --
> http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> email EraseMElistservmitvma.mit.edu with SET PICList DIGEST in the body

>
> Permanent magnets can have significantly differing strengths due to the way
> they are magnetised. Hall effect sensors have significant tempco, and of
> course there is the earth's magnetic field, and local magnetic fields to
> contend with. This would also be somewhat expensive.
>

zero point adjustment is the magic word... but you're right, this is awful to
realize.

> My money's still on my earlier suggestion of a simple tuned circuit in each
> piece, and coils etched into a PCB under the board - cheap & easy to build.
> Even if you couldn't figure out a way to do it in a matrix, the switching
> would only need nine 8-1 analogue multiplexers (ultra-cheap 4000 CMOS) ,
> and the detection hardware would be simple and cheap - PC generates the
> frequencies, and a simple detector generates a DC level for the PIC ADC to
> detect the presence of a piece - maybe a handful of passives and an opamp.
> Can't see how you could get much cheaper than this.
>
> You could even make it retro-fittable to existing pieces, as you could usea
> PCB coil with a cutout for the capacitor, forming a simple disc shape that
> can be stuck to the bottom of the piece.
>
> Proximity of the piece will not cause false detection (e.g. if piece
> hovers) - you are simply looking for a resonance at one of 12 frequencies.
> The position of the piece within the square should also not be much of a
> problem. The proximity of the board coil to the (pcb) coil in the base of
> the piece would be so close (2-3mm max) that cross-coupling to an adjacent
> piece should not be an issue.
>
> Even if PCB coils turn out to not give enough coupling at a suitable
> frequency, small surface-mount inductors could be used - still cheap, and
> very good coupling - I've recently used these to do an inductive datalink
> into a potted product.
>

I've got another Idea... Resonant frequencies aren't that perfect (lot of
tuning and choosing the right frequency for each pice without constructing
overcutting resonants).
But we can still go forth with coils. We can put a resonant coil (only one
frequency for all) in each figure in parallel to a load resistor.
If we choose different load resistors, then each figure would draw a different
amount of power from the coils under the chessboard, this could be
measured... You have to admit, that this is a little bit easier than using
multiple resonant frequencies, that all want to be scanned on each square of
the board.

Well, a bar code scanner doesn't work reliable enough (ya know, you're in one of those supermarkets and the lady has to type in your numbers by hand, because that damn scanner doesn't work properly).
And it is a lot of precisely optics needed to build a bar code scanner like that. At least the parts are expensive and fragile (exspecially the first surface mirrors that are needed to redirect laser beams).

For only 32 pieces the bar-codes can be a series of concentric rings with larger cross
sectional areas than standard bar codes. First surface mirrors on a pizeo driver need not
be super expensive (surplus parts) lazer diodes are cheep enough..glass chess board...

Could use a camera under the chess board with a frame grabber and analyze the pixels. Did
a tracking system that way once...

Am Donnerstag, 11. März 2004 02:32 schrieben Sie:
> For only 32 pieces the bar-codes can be a series of concentric rings with
> larger cross sectional areas than standard bar codes. First surface mirrors
> on a pizeo driver need not be super expensive (surplus parts) lazer diodes
> are cheep enough..glass chess board...
>
> Could use a camera under the chess board with a frame grabber and analyze
> the pixels. Did a tracking system that way once...
>
> Vern

This sounds interesting (the tracking system, do you have that project online??), but is still a high effort, and expensive. And you have to remember that chess boards have dark squares, too!

>
> Am Donnerstag, 11. März 2004 02:32 schrieben Sie:
> > For only 32 pieces the bar-codes can be a series of concentric rings with
> > larger cross sectional areas than standard bar codes. First surface mirrors
> > on a pizeo driver need not be super expensive (surplus parts) lazer diodes
> > are cheep enough..glass chess board...
> >
> > Could use a camera under the chess board with a frame grabber and analyze
> > the pixels. Did a tracking system that way once...
> >
> > Vern
>
> This sounds interesting (the tracking system, do you have that project
> online??), but is still a high effort, and expensive. And you have to
> remember that chess boards have dark squares, too!
>
> Do.Pe.
>
> --
> http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> email spamBeGonelistservSTOPspamEraseMEmitvma.mit.edu with SET PICList DIGEST in the body

Lets try a new angle on this, just to get the minds smoking. How about
an overhead video camera and optical identifcation.
It eliminates all the contact problems, parts etc. just a video camera
and ??? MB of software. It will solve the tipped over and moved by
accident
piece problems ( sound an alarm for non legal move). You just need
peices that are shaped different enough to be identifed. It also has
less hard ware to
go wrong.

> Robert Rolf wrote:
>
>> What Jinx suggested, a resonant coil under each square
>
> [...]
>
>> And the idea of using hall effect and having different
>
> [...]
>
>> One could also use an IR transparent base and a reflective
>
> [...]
>
> This are the three methods we have.
>
> > Do let us know what you discover works best.
>
> Sure, if we continue with this project. Of course it will need a PIC too.
>
> > My bet is hall effect with enough variance in the
> > magnet strengths that position error is within the
> > 12 quantizing levels you'd need. Or IR.
>
> I agree. I do not like too much the radio method due to the
> interferences, either internal between chessman's coils, either external
> noises (mobile phones).
>
> The IR needs a special board, what it gives it a second place. On the
> first one is the hall effect. May be because I have never play with it
> and do not know its limitations.
>
>> What I don't understand is why you need to know the 'starting
>> position'.
>
>
> Is needed for the chessboard, not for 'me'. If it doesn't recognize the
> pieces you have to tell it where is which.
>
>> I thought all chess games start with the pieces
>> in the same position, so all you need to detect is which
>
>
> Er..., not. What about a resumed match ?, what about to study a certain
> position ?
>
> Cheers,
> Diego.
>
> --
> http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> email EraseMElistservEraseMEmitvma.mit.edu with SET PICList DIGEST in the body
>

Am Donnerstag, 11. März 2004 02:56 schrieben Sie:
> All I have on line of this system is a picture of the finished telescope.
> The project was done in 1994. So there isn't much on line from that era.
>
> Vern
>

And what about some other stuff about picture/shape recognition?
Anyway, put the link to your page here, please ;-)

Am Donnerstag, 11. März 2004 02:59 schrieben Sie:
> Lets try a new angle on this, just to get the minds smoking. How about
> an overhead video camera and optical identifcation.
> It eliminates all the contact problems, parts etc. just a video camera
> and ??? MB of software. It will solve the tipped over and moved by
> accident
> piece problems ( sound an alarm for non legal move). You just need
> peices that are shaped different enough to be identifed. It also has
> less hard ware to
> go wrong.
>

Okay, now let's take off from earth...
Build a holographic system (some white clouds over the chessboard) and use laser beams of different color to project the chessboard and the figures into these clouds. The player has to enter his moves manually with a keyboard, and the deep blue style computer projects the move onto the "screen" and makes his own move (good look)...

Jinx wrote:
>
> > On a timed match, there is no extra time for plugging the pieces :)
>
> Which might rule out some options unless you have the PIC
> wait for a settling time. For instance, as a magnet approaches
> a sensor the sensor will see an increasing field. When does the
> PIC decide that the piece has been placed ? Perhaps when the

0.25 seconds without change?

> timer is struck ? That would also eliminate false positives from
> hovering-but-unplaced pieces

A hovering piece will have a fluctuating measurement due to tremor.
No human could hold a hovering piece in position to 1 part in 256.
A landed piece would be flat line plus or minus A/D noise.

Hall tempco is easily handled by having a 'reference' hall sensor that
is magnetically shielded but at same temperature as the others.
And you use an average of the 'empty' squares to compensate for
any stray fields. A minimum of 50% of the squares
will always be empty after all so no 'tempco' unit is needed in fact.

Halls can also be multiplexed (8x8) using their power leads
and diode coupling their outputs (think backwards wired-or)
with a reference diode to compensate diode tempco effects.
(differential op amp).

>>
>> Permanent magnets can have significantly differing strengths due to the way
>> they are magnetised. Hall effect sensors have significant tempco, and of
>> course there is the earth's magnetic field, and local magnetic fields to
>> contend with. This would also be somewhat expensive.
>>
>
>zero point adjustment is the magic word... but you're right, this is awful to
>realize.
>
>> My money's still on my earlier suggestion of a simple tuned circuit in each
>> piece, and coils etched into a PCB under the board - cheap & easy to build.
>> Even if you couldn't figure out a way to do it in a matrix, the switching
>> would only need nine 8-1 analogue multiplexers (ultra-cheap 4000 CMOS) ,
>> and the detection hardware would be simple and cheap - PC generates the
>> frequencies, and a simple detector generates a DC level for the PIC ADC to
>> detect the presence of a piece - maybe a handful of passives and an opamp.
>> Can't see how you could get much cheaper than this.
>>
>> You could even make it retro-fittable to existing pieces, as you could usea
>> PCB coil with a cutout for the capacitor, forming a simple disc shape that
>> can be stuck to the bottom of the piece.
>>
>> Proximity of the piece will not cause false detection (e.g. if piece
>> hovers) - you are simply looking for a resonance at one of 12 frequencies.
>> The position of the piece within the square should also not be much of a
>> problem. The proximity of the board coil to the (pcb) coil in the base of
>> the piece would be so close (2-3mm max) that cross-coupling to an adjacent
>> piece should not be an issue.
>>
>> Even if PCB coils turn out to not give enough coupling at a suitable
>> frequency, small surface-mount inductors could be used - still cheap, and
>> very good coupling - I've recently used these to do an inductive datalink
>> into a potted product.
>>
>
>I've got another Idea... Resonant frequencies aren't that perfect (lot of
>tuning and choosing the right frequency for each pice without constructing
>overcutting resonants).
>But we can still go forth with coils. We can put a resonant coil (only one
>frequency for all) in each figure in parallel to a load resistor.
>If we choose different load resistors, then each figure would draw a different
>amount of power from the coils under the chessboard, this could be
>measured... You have to admit, that this is a little bit easier than using
>multiple resonant frequencies, that all want to be scanned on each square of
>the board.

No it isn't.
We are back to all the possible variations of signal strength giving false results, in particular
distance from piece to coil. With different resonant frequencies, we only have to detect presence or absence of loading at a
given frequency for each square, which should give a much more reliable and definite result.

>Lets try a new angle on this, just to get the minds smoking. How about
>an overhead video camera and optical identifcation.
>It eliminates all the contact problems, parts etc. just a video camera
>and ??? MB of software. It will solve the tipped over and moved by
>accident
>piece problems ( sound an alarm for non legal move). You just need
>peices that are shaped different enough to be identifed. It also has
>less hard ware to
>go wrong.
>
>Bob
A camera under the board would be better. If the board was made IR-transparent (easy), and you could
handle the optics to project the image onto a VGA sensor, this gives 30x30 pixels per square, which
should be plenty for recognition.
I think the main problem would be making the board acceptably thin.
Still more expensive than an array of coils though...!

> on a specified square and whether it is a bishop, queen. pawn,... etc. Or do
> you want to create a record of all of the moves of all of the peices on the
> respective squares so as to reconstruct the game.

Well, two things I understood from my chess player friend: to play
against a program (the chessboard acts as the interface with the
program, many players will prefer a real board than a computer monitor)
and to show a match on a monitor and/or Internet (no human intervention
to setup the pieces, although this can be down by tracking the pieces
movement from their inital setup, I explained yesterday why would be
preferable to detect which piece is where).

>>>
>>> Permanent magnets can have significantly differing strengths due to the way
>>> they are magnetised. Hall effect sensors have significant tempco, and of
>>> course there is the earth's magnetic field, and local magnetic fields to
>>> contend with. This would also be somewhat expensive.
>>>
>>
>>zero point adjustment is the magic word... but you're right, this is awful to
>>realize.
>>
>>> My money's still on my earlier suggestion of a simple tuned circuit in each
>>> piece, and coils etched into a PCB under the board - cheap & easy to build.
>>> Even if you couldn't figure out a way to do it in a matrix, the switching
>>> would only need nine 8-1 analogue multiplexers (ultra-cheap 4000 CMOS) ,
>>> and the detection hardware would be simple and cheap - PC generates the
>>> frequencies, and a simple detector generates a DC level for the PIC ADC to
>>> detect the presence of a piece - maybe a handful of passives and an opamp.
>>> Can't see how you could get much cheaper than this.
>>>
>>> You could even make it retro-fittable to existing pieces, as you could usea
>>> PCB coil with a cutout for the capacitor, forming a simple disc shape that
>>> can be stuck to the bottom of the piece.
>>>
>>> Proximity of the piece will not cause false detection (e.g. if piece
>>> hovers) - you are simply looking for a resonance at one of 12 frequencies.
>>> The position of the piece within the square should also not be much of a
>>> problem. The proximity of the board coil to the (pcb) coil in the base of
>>> the piece would be so close (2-3mm max) that cross-coupling to an adjacent
>>> piece should not be an issue.
>>>
>>> Even if PCB coils turn out to not give enough coupling at a suitable
>>> frequency, small surface-mount inductors could be used - still cheap, and
>>> very good coupling - I've recently used these to do an inductive datalink
>>> into a potted product.
>>>
>>

>>tuning and choosing the right frequency for each pice without constructing
>>overcutting resonants).
>>But we can still go forth with coils. We can put a resonant coil (only one
>>frequency for all) in each figure in parallel to a load resistor.
>>If we choose different load resistors, then each figure would draw a different
>>amount of power from the coils under the chessboard, this could be
>>measured... You have to admit, that this is a little bit easier than using
>>multiple resonant frequencies, that all want to be scanned on each square of
>>the board.

> No it isn't.
> We are back to all the possible variations of signal strength giving false results, in particular
> distance from piece to coil.
> With different resonant frequencies, we only have to detect presence or absence of loading at a
> given frequency for each square, which should give a much more reliable and definite result.

Why make it so complicated? You don't need mutiple driving frequencies. Just excite the coil
under each square with a step function and look for the ringing frequency. Some amplification
boosts the signal to the amplitude that can be detected with an analog comparator and
timer/capture module.

>> From: Mike Harrison[SMTP:mikeEraseMEWHITEWING.CO.UK]
>> Sent: Thursday, March 11, 2004 4:40 AM
>> To: RemoveMEPICLISTEraseMEspam_OUTMITVMA.MIT.EDU
>> Subject: Re: [PIC:] Chessboard (sensor)
>
>> On Thu, 11 Mar 2004 02:19:57 +0100, you wrote:
>
>>>>
>>>> Permanent magnets can have significantly differing strengths due to the way
>>>> they are magnetised. Hall effect sensors have significant tempco, and of
>>>> course there is the earth's magnetic field, and local magnetic fields to
>>>> contend with. This would also be somewhat expensive.
>>>>
>>>
>>>zero point adjustment is the magic word... but you're right, this is awful to
>>>realize.
>>>
>>>> My money's still on my earlier suggestion of a simple tuned circuit in each
>>>> piece, and coils etched into a PCB under the board - cheap & easy to build.
>>>> Even if you couldn't figure out a way to do it in a matrix, the switching
>>>> would only need nine 8-1 analogue multiplexers (ultra-cheap 4000 CMOS) ,
>>>> and the detection hardware would be simple and cheap - PC generates the
>>>> frequencies, and a simple detector generates a DC level for the PIC ADC to
>>>> detect the presence of a piece - maybe a handful of passives and an opamp.
>>>> Can't see how you could get much cheaper than this.
>>>>
>>>> You could even make it retro-fittable to existing pieces, as you could usea
>>>> PCB coil with a cutout for the capacitor, forming a simple disc shape that
>>>> can be stuck to the bottom of the piece.
>>>>
>>>> Proximity of the piece will not cause false detection (e.g. if piece
>>>> hovers) - you are simply looking for a resonance at one of 12 frequencies.
>>>> The position of the piece within the square should also not be much of a
>>>> problem. The proximity of the board coil to the (pcb) coil in the base of
>>>> the piece would be so close (2-3mm max) that cross-coupling to an adjacent
>>>> piece should not be an issue.
>>>>
>>>> Even if PCB coils turn out to not give enough coupling at a suitable
>>>> frequency, small surface-mount inductors could be used - still cheap, and
>>>> very good coupling - I've recently used these to do an inductive datalink
>>>> into a potted product.
>>>>
>>>
>.I've got another Idea... Resonant frequencies aren't that perfect (lot of
>>>tuning and choosing the right frequency for each pice without constructing
>>>overcutting resonants).
>>>But we can still go forth with coils. We can put a resonant coil (only one
>>>frequency for all) in each figure in parallel to a load resistor.
>>>If we choose different load resistors, then each figure would draw a different
>>>amount of power from the coils under the chessboard, this could be
>>>measured... You have to admit, that this is a little bit easier than using
>>>multiple resonant frequencies, that all want to be scanned on each square of
>>>the board.
>
>> No it isn't.
>> We are back to all the possible variations of signal strength giving false results, in particular
>> distance from piece to coil.
>> With different resonant frequencies, we only have to detect presence or absence of loading at a
>> given frequency for each square, which should give a much more reliable and definite result.
>
>Why make it so complicated? You don't need mutiple driving frequencies. Just excite the coil
>under each square with a step function and look for the ringing frequency. Some amplification
>boosts the signal to the amplitude that can be detected with an analog comparator and
>timer/capture module.
>
>John Power

That assumes your tuned circuit has enough Q to get enough rings to measure the frequency. It is
also possibly more susceptible to noise. Generating a sweep is easy enough to do, and then you are
looking at a simple yes/no decision based on the coil loading level - you could probably even just
measure the DC current into the output driver.
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